CN113604137B - Scratch-resistant epoxy modified polyester back paint for coiled material with high coating rate and preparation method thereof - Google Patents

Scratch-resistant epoxy modified polyester back paint for coiled material with high coating rate and preparation method thereof Download PDF

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CN113604137B
CN113604137B CN202110364057.XA CN202110364057A CN113604137B CN 113604137 B CN113604137 B CN 113604137B CN 202110364057 A CN202110364057 A CN 202110364057A CN 113604137 B CN113604137 B CN 113604137B
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polyester resin
modified polyester
epoxy modified
resin
scratch
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CN113604137A (en
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李扬
冯春苗
吴奎录
周春利
蒋旭
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CNOOC Energy Technology and Services Ltd
CNOOC Changzhou EP Coating Co Ltd
CNOOC Changzhou Paint and Coatings Industry Research Institute Co Ltd
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CNOOC Energy Technology and Services Ltd
CNOOC Changzhou EP Coating Co Ltd
CNOOC Changzhou Paint and Coatings Industry Research Institute Co Ltd
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    • CCHEMISTRY; METALLURGY
    • C09DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09DCOATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D167/00Coating compositions based on polyesters obtained by reactions forming a carboxylic ester link in the main chain; Coating compositions based on derivatives of such polymers
    • C09D167/02Polyesters derived from dicarboxylic acids and dihydroxy compounds
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08GMACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/91Polymers modified by chemical after-treatment
    • C08G63/914Polymers modified by chemical after-treatment derived from polycarboxylic acids and polyhydroxy compounds
    • C08G63/916Dicarboxylic acids and dihydroxy compounds
    • CCHEMISTRY; METALLURGY
    • C09DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09DCOATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D5/00Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
    • C09D5/08Anti-corrosive paints
    • CCHEMISTRY; METALLURGY
    • C09DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09DCOATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D7/00Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
    • C09D7/40Additives
    • C09D7/60Additives non-macromolecular
    • C09D7/61Additives non-macromolecular inorganic
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08KUse of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00Use of inorganic substances as compounding ingredients
    • C08K3/18Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20Oxides; Hydroxides
    • C08K3/22Oxides; Hydroxides of metals
    • C08K2003/2237Oxides; Hydroxides of metals of titanium
    • C08K2003/2241Titanium dioxide
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08KUse of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00Use of inorganic substances as compounding ingredients
    • C08K3/30Sulfur-, selenium- or tellurium-containing compounds
    • C08K2003/3045Sulfates

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  • Health & Medical Sciences (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Paints Or Removers (AREA)

Abstract

The invention discloses a scratch-resistant epoxy modified polyester back paint for a high-coating-rate coiled material, which comprises the following components in parts by weight: 20-35 parts of epoxy modified polyester resin, 3-10 parts of branched polyester resin, 4-10 parts of curing agent, 20-35 parts of pigment and filler, 0.2-1 part of wax powder, 2-4 parts of auxiliary agent and 15-30 parts of mixed solvent; wherein the epoxy modified polyester resin is prepared by ring-opening polymerization reaction of epoxy resin and linear carboxyl-terminated polyester resin prepolymer. The invention also discloses a preparation method of the scratch-resistant epoxy modified polyester back paint for the coiled material with the high coating rate.

Description

Scratch-resistant epoxy modified polyester back paint for coiled material with high coating rate and preparation method thereof
Technical Field
The invention relates to the technical field of coil coating, in particular to scratch-resistant epoxy modified polyester back paint for a high-coating-rate coil and a preparation method thereof.
Background
The home appliance board market has been developed vigorously in recent years as a higher and newer application market for precoated coil coatings. Compared with the traditional building board, the performance requirement of the back paint of the household electric board is higher. The back paint for the household appliance plate usually adopts a single coating, has a thin film, mainly plays a role in protecting the back surface, requires a paint film to have good salt mist resistance, foaming layer sticking performance, adhesion resistance, processing performance and the like, and has low requirements on decoration and durability. The technical content of high-performance back-lacquers for household electrical panels is therefore rather high.
In consideration of the low requirement of weather resistance of the coil back paint and the general requirement of decorative protection, the important consideration is focused on the protection and the later processing property, and the requirement that the color steel plate back plate meets the foaming and the gluing is also the most important. The common coil back paint mainly comprises epoxy resin, polyester resin and epoxy mixed polyester resin systems. The epoxy back paint has good butanone (MEK) wiping resistance, high hardness, excellent adhesive force, good performance of adhering a foaming layer and good salt spray resistance, but has the defect of poor flexibility; although the common polyester back paint has good flexibility, the MEK wiping resistance is slightly poor, and the adhesive force and the pressure resistance are relatively poor; in the actual use process, in order to meet the market demand and make up the performance defects of epoxy resin coatings and polyester resin coatings, a method of blending polyester resin with epoxy resin is often used, and the coil back paint of epoxy blended polyester resin has the performance between the two, so that the precoated metal coil coating back paint with excellent comprehensive performance is obtained. Therefore, the back paint of the common coiled material generally adopts a method of blending polyester resin and epoxy resin, namely the two components are respectively added into the back paint coating formula, so that the back paint has the characteristics of polyester and epoxy at the same time, but the blending system has general matching performance, and in the actual use process, the cold blending and epoxy resin addition has a plurality of problems, such as T-bend performance reduction after blending, poor flexibility, addition fluctuation between batches, obvious storage layering and the like.
At present, the back paint of the household electrical panel is cut and stacked after being coated and rolled, and in the long-distance transportation process or the carrying process, the force of relative displacement can be generated, so that the back paint and the finish paint are reversely adhered and have pressure marks, and even the surface of a paint film is scratched to remove the paint, so that the loss is caused. Usually, when the protective post-processing property requirement is ensured, in order to improve the scratch resistance of the coating, macromolecular epoxy resin main body film forming materials are adopted, so that the mechanical strength, the hardness and the scratch resistance of a paint film are enhanced. And the epoxy coil coating is the best product recognized by the market at present for the later foaming performance. However, with the increasingly fierce market competition, the requirements of customers on the performance evaluation of production lines are improved, the updating of processing dies and the coating rate, the environmental protection and the better processability of the coating become key factors of the product competitiveness, and the disadvantages of slightly poor hard processability of a paint film are gradually shown due to the low solid content and the low coating rate of the epoxy resin. In view of the above, there is a need to develop a high-coating rate coil back paint with high solid content, high hardness, excellent adhesion and pressure resistance, excellent mechanical properties, and excellent wear resistance and scratch resistance.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a scratch-resistant epoxy modified polyester back paint for a coiled material with a high coating rate and a preparation method thereof.
The invention provides a scratch-resistant epoxy modified polyester back paint for a high-coating-rate coiled material, which comprises the following components in parts by weight:
Figure BDA0003006692250000021
Figure BDA0003006692250000031
wherein the epoxy modified polyester resin is prepared by ring-opening polymerization reaction of epoxy resin and linear carboxyl-terminated polyester resin prepolymer.
In one embodiment, the preparation method of the epoxy modified polyester resin comprises the following steps:
in the presence of a catalyst, firstly, carrying out esterification reaction on dihydric alcohol and dibasic acid to obtain a linear carboxyl-terminated polyester resin prepolymer;
and (2) carrying out ring-opening polymerization reaction on the linear carboxyl-terminated polyester resin prepolymer prepared in the step (1), dihydric alcohol and epoxy resin under the action of a catalyst to obtain the epoxy modified polyester resin containing linear flexible chains.
In one embodiment, in the esterification reaction in the step (1), the ratio of the number of moles of hydroxyl groups contained in the diol to the number of moles of carboxyl groups contained in the diacid is 1: 1.1-1.5.
In one embodiment, in the ring-opening polymerization reaction of step (2), the ratio of the number of moles of carboxyl groups contained in the linear carboxyl-terminated polyester resin prepolymer to the number of moles of epoxy groups in the epoxy resin is 1: 0.6-0.9.
In one embodiment, the dibasic acid is one or more of phthalic anhydride, isophthalic acid, terephthalic acid, hexahydrophthalic anhydride, adipic acid, 1, 4-cyclohexanedicarboxylic acid and 1, 2-cyclohexanedicarboxylic acid; the dihydric alcohol is one or a mixture of more of neopentyl glycol, methyl propanediol, 1, 4-butanediol, 1, 6-hexanediol, hydroxypivalic acid neopentyl glycol monoester, 3-methyl-1, 5-pentanediol, ethyl butyl propanediol, 1, 4-cyclohexanedimethanol, 1, 2-cyclohexanedimethanol and 2,2, 4-trimethyl-1, 3-pentanediol.
In one embodiment, the esterification reaction conditions in step (1) are: slowly heating at the speed of 10 ℃/h until the temperature reaches 140 ℃ for reflux reaction, preserving the heat at 200 ℃ for 1-2 hours, slowly heating to 230 ℃ for heat preservation reaction until the measured acid value is stable and unchanged; the conditions of the ring-opening polymerization reaction in the step (2) are as follows: slowly heating at the speed of 10 ℃/h, preserving heat for 2-3 hours at 140 ℃, slowly heating to 200 ℃, preserving heat for 1-2 hours, slowly heating to 230 ℃, preserving heat, reacting until the acid value is less than 5mgKOH/g, cooling to below 180 ℃, and vacuumizing to remove residual water and micromolecule alcohol.
In one embodiment, the esterification catalyst is monobutyl tin oxide.
In one embodiment, the epoxy resin is a low molecular weight epoxy resin, and the epoxy value of the epoxy resin is 0.10-0.55mol/100 g.
In one embodiment, the epoxy resin is a solvent-free 100% solids liquid or solid.
In one embodiment, the epoxy resin is selected from at least any one of commercially available E44, E51, NPES-901, CYD011, CYD014, CYD144, and EPlKOTE 828 EL.
In one embodiment, the branched polyester resin is a branched saturated polyester resin with a terminal hydroxyl functional group, and has an acid value of 0-3mgKOH/g, a number average molecular weight of 2000-5000, and a hydroxyl value of 30-100 mgKOH/g.
In one embodiment, the branched polyester resin is selected from the group consisting of commercially available spacious new materials, model number of CL271, CL151, CL150, C7621, G9630, CB226, CD426, and korean SK, model number of ES710, ES 750.
In one embodiment, the mass ratio of the branched polyester resin to the binder is 10: 90-20: 80; wherein, the base material comprises epoxy modified polyester resin, branched polyester resin and a curing agent.
In one embodiment, the curing agent is an amino resin; the amino resin is at least one of methylated urea-formaldehyde resin, butylated urea-formaldehyde resin, fully methylated amino resin, partially methylated amino resin, butylated amino resin and high imino amino resin; the mass ratio of the curing agent to the base material is 15:85-20: 80.
In one embodiment, the amino resin is selected from at least any one of CYMEL303, CYMEL325, ETERMINO 9115-60-2 and CYMEL 1158 of Cyanorthe, and Resimene-747 and Resimene-717 of Vorino.
In one embodiment, the wax powder is at least one of synthetic wax, fluorine-modified polyethylene wax and fluorine-modified synthetic wax.
In one embodiment, the wax powder is at least one selected from MP-22XF, MP-28XF, Polyfluo150, Polyfluo523XF, Synfluo178XF and Synfluo180XF from US micropowder.
In one embodiment, the pigment and filler is at least one of titanium dioxide, carbon black, iron oxide red, iron oxide yellow, precipitated barium sulfate, talcum powder and organic bentonite.
In one embodiment, the auxiliary agent is at least one of a dispersant, a defoamer, a leveling agent, a curing catalyst and an adhesion promoter.
In one embodiment, the dispersant is selected from at least one of AFCONA model of AFCONA-4010, AFCONA-4017, AFCONA-4047, AFCONA-4060, AFCONA-4070, AFCONA-4080, AFCONA-4072, AFCONA-4077 and AFCONA-4565.
In one embodiment, the defoaming agent is a non-silicon system defoaming agent and is selected from at least one of BYK model BYK-054, BYK352, BYK-057, BYK-1788 and BYK-1795.
In one embodiment, the leveling agent is a non-silicon system leveling agent and is selected from at least one of AFCONA model of AFCONA-3277, AFCONA-3670, AFCONA-3700, AFCONA-3750, AFCONA-3773, AFCONA-3775, AFCONA-3777 and AFCONA-3779.
In one embodiment, the curing catalyst comprises an acid catalyst selected from at least any one of NACURE 1419, NACURE 1051, NACURE 2500, and NACURE 5225.
In one embodiment, the adhesion promoter is a phosphate modified polymer selected from at least one of PAE206, DS-600, Lubrizol 2063, Tech-7205, and ADP.
In one embodiment, the mixed solvent is at least one of butanol, propylene glycol methyl ether acetate, ethylene glycol butyl ether, cyclohexanone, xylene, an S-100# aromatic solvent, an S-150# aromatic solvent and a dibasic ester DBE.
The invention also provides a preparation method of the scratch-resistant epoxy modified polyester back paint for the coiled material with the high coating rate, which comprises the following steps:
step (1): mixing 30-50% of epoxy modified polyester resin, a dispersant, pigment and filler and wax powder, adding 30-50% of mixed solvent, grinding to obtain slurry, wherein the slurry is sanded to be less than 20 mu m;
step (2): adding the rest of epoxy modified polyester resin, branched polyester resin and the rest of auxiliary agent into the slurry and mixing; and then adding the curing agent and the residual mixed solvent, mixing and filtering to obtain the epoxy modified polyester back paint.
Has the advantages that:
1. the method of the invention carries out epoxy modification on the polyester resin in advance, and then takes the epoxy modified polyester resin as a base material to prepare the precoated coil coating back paint. In the resin synthesis process, the epoxy modified polyester resin is prepared by carrying out ring-opening polymerization reaction on epoxy resin and linear carboxyl-terminated polyester resin prepolymer, and the epoxy modified polyester resin organically combines the advantages of the polyester resin and the epoxy resin and has much stronger performances such as adhesive force, flexibility, boiling water resistance, humidity and heat resistance and other mechanical performances than back paint prepared by a blending method.
2. The epoxy modified polyester resin prepared by the invention obviously improves the flexibility and T-bend performance under the condition of ensuring the hardness of a back paint film, increases the crosslinking density of a paint system and enhances the corrosion resistance, and the epoxy modified polyester resin can reduce the manufacturing procedures of the paint and reduce the variety of added raw materials, thereby reducing the production control cost, increasing the stability among batches and reducing the quality risk.
3. And (3) carrying out ring-opening reaction on the linear carboxyl-terminated polyester resin prepolymer and epoxy resin to obtain the epoxy modified polyester resin. The types of the dihydric alcohol, the dibasic acid and the epoxy resin are changed, so that the resins with different molecular structures and performances can be obtained, and the adjustability of the molecular structure is realized.
4. The scratch-resistant epoxy modified polyester back paint for the coiled material with the high coating rate has the characteristics of high coating amount and good processability, and the obtained back paint film has the characteristics of good adhesiveness, processability, high gloss, good surface smoothness, good scratch resistance effect, excellent polyurethane foaming and the like, and is suitable for the back of various coated steel plates.
5. The scratch-resistant epoxy modified polyester back paint for the coiled material with the high coating rate provided by the invention has the solid content of more than 65%, and the coating weight of 380m2More than mu per kg, the coating weight of the traditional epoxy back paint is 280m2The coating weight is improved by about 35 percent per kg mu.
Detailed Description
The technical solution of the present invention is further illustrated by the following examples. The scope of the present invention is not limited to the specific embodiments but is defined by the scope of the claims.
In the case where the objects of the present invention are illustrated and explained by the following examples, the components of the composition are all explained on the general standard of parts by weight. In the present invention, the term "part" is used in the same sense as "part by weight" in the examples, unless otherwise specified, for the sake of brevity.
The epoxy-modified polyester resins A to T described in examples 1 to 60 were prepared as follows:
step (1): the I and II (see table 1 in detail) and xylene as solvent in the formula are put into a clean reaction bottle provided with a stirrer, a thermometer, a water separator, a fractionating column and an inert gas inlet, and stirring is started while introducing inert gas after the materials are molten. And (3) slowly heating the materials at the speed of 10 ℃/h until the materials are refluxed at the temperature of 140 ℃, preserving the heat for 1-2 hours at the temperature of 200 ℃, slowly heating to the temperature of 230 ℃, preserving the heat, reacting until the acid value is stable and unchanged, and cooling to obtain the linear carboxyl-terminated polyester prepolymer.
Step (2): and (2) continuously adding the III, IV (see table 1) and a solvent xylene in the formula into the reaction bottle on the basis of the step (1), starting stirring after the materials are molten, and introducing inert gas. Slowly heating the material at the speed of 10 ℃/h, preserving heat for 2-3 hours at 140 ℃, slowly heating to 200 ℃, preserving heat for 1-2 hours, slowly heating to 230 ℃, preserving heat, reacting until the measured acid value is less than 5mgKOH/g, cooling to below 180 ℃, and vacuumizing to remove residual water and micromolecule alcohol. And continuously cooling to about 150 ℃, adding a mixed solvent of ethylene glycol ethyl ether acetate, an S-1000 aromatic solvent and a DBE solvent (mixing the three reagents in any proportion), fully stirring in the process, and filtering to obtain a filtrate, namely the epoxy modified polyester resin.
TABLE 1 charging conditions of materials in step (1) and step (2)
Figure BDA0003006692250000081
Figure BDA0003006692250000091
Figure BDA0003006692250000101
The scratch-resistant epoxy-modified polyester back paints for high-coating rate coils described in examples 1 to 60 were prepared by the following procedure:
step (1): mixing 30-50% of epoxy modified polyester resin, a dispersant, pigment and filler and wax powder, adding 30-50% of mixed solvent, grinding to obtain slurry, wherein the slurry is sanded to be less than 20 mu m; step (2): adding the rest of epoxy modified polyester resin, branched polyester resin and the rest of auxiliary agent into the slurry and mixing; and then adding the curing agent and the residual mixed solvent, mixing and filtering to obtain the epoxy modified polyester back paint.
TABLE 2 charging conditions of the materials in step (1) and step (2) of examples 1 to 60
Figure BDA0003006692250000102
Figure BDA0003006692250000111
Figure BDA0003006692250000121
Figure BDA0003006692250000131
Figure BDA0003006692250000141
Figure BDA0003006692250000151
Figure BDA0003006692250000161
Figure BDA0003006692250000171
Figure BDA0003006692250000181
Figure BDA0003006692250000191
Figure BDA0003006692250000201
Figure BDA0003006692250000211
Figure BDA0003006692250000221
Coating plate-making process
The epoxy modified polyester back paint obtained is coated on a pretreated galvanized steel plate with the thickness of 12cm multiplied by 15cm multiplied by 0.5mm by a wire bar roller, and is baked in an oven at the temperature of 300 ℃ for 40s, the metal plate temperature PMT: 224 ℃ to give a back-coat layer with a film thickness of 5-7 μm.
The products of examples 1 to 60 all meet the quality specifications of Table 3.
TABLE 3 New Performance test standards for the products of examples 1-60
Figure BDA0003006692250000222
Figure BDA0003006692250000231
Note: compression resistance experiment: the ordinary surface paint plate is closely attached to the back paint plate, the temperature is 90 ℃, the pressure is equivalent to 20t of steel coil, and after 24h, whether the surface paint plate and the back paint plate have indentations (evaluation standards: no indentation, slight indentation, indentation and severe indentation) is judged; rub-resistant experiment: namely, a relative displacement experiment is carried out, namely, the force of relative displacement is generated by closely adhering finish paint to a back paint plate in the transportation process of a simulated color-coated coil, a common finish paint plate is selected to be closely adhered to the back paint plate, and the finish paint plate and the back paint plate are rubbed with each other under the force of 10kg at the temperature of 50 ℃ (evaluation criteria: no paint falling, slight paint falling, paint falling and severe paint falling).
The solid content of the epoxy modified polyester back paint for the coiled material prepared by the invention can reach more than 65 percent, and the coating weight can reach 380m2The coating weight is improved by about 35 percent compared with the coating weight of the traditional macromolecular epoxy back paint by more than kg.mu; the obtained back paint film has the characteristics of good adhesiveness, processability, good surface smoothness, good scratch resistance effect, excellent polyurethane foaming and the like, and is suitable for the back of various coated steel plates. The preparation method is simple, environment-friendly and easy for large-scale production.
It should be understood that the above examples are only preferred embodiments of the present invention, and are intended to illustrate the detailed description of the technical solutions of the present invention, and not to limit the scope of the present invention. It should be noted that: after reading the present invention, one skilled in the art can make several modifications and equivalents without departing from the principle of the present invention, and such modifications and equivalents fall within the scope of the present invention as defined in the claims.

Claims (7)

1. The scratch-resistant epoxy modified polyester back paint for the coiled material with the high coating rate is characterized by comprising the following components in parts by weight:
Figure FDA0003488446770000011
wherein the epoxy modified polyester resin is prepared by ring-opening polymerization reaction of epoxy resin and linear carboxyl-terminated polyester resin prepolymer;
the preparation method of the epoxy modified polyester resin comprises the following steps:
in the presence of a catalyst, firstly, carrying out esterification reaction on dihydric alcohol and dibasic acid to obtain a linear carboxyl-terminated polyester resin prepolymer;
performing ring-opening polymerization reaction on the linear carboxyl-terminated polyester resin prepolymer prepared in the step (1), dihydric alcohol and epoxy resin under the action of a catalyst to obtain epoxy modified polyester resin containing a linear flexible chain;
the esterification reaction conditions in the step (1) are as follows: slowly heating at the speed of 10 ℃/h until the temperature reaches 140 ℃ for reflux reaction, preserving the heat at 200 ℃ for 1-2 hours, slowly heating to 230 ℃ for heat preservation reaction until the measured acid value is stable and unchanged; the conditions of the ring-opening polymerization reaction in the step (2) are as follows: slowly heating at the speed of 10 ℃/h, preserving heat for 2-3 hours at 140 ℃, slowly heating to 200 ℃, preserving heat for 1-2 hours, slowly heating to 230 ℃, preserving heat, reacting until the measured acid value is less than 5mgKOH/g, cooling to below 180 ℃, and vacuumizing to remove residual water and micromolecular alcohol;
the branched polyester resin is a branched saturated polyester resin with a terminal hydroxyl functional group, the acid value of the branched saturated polyester resin is 0-3mgKOH/g, the number average molecular weight of the branched saturated polyester resin is 2000-5000, and the hydroxyl value of the branched saturated polyester resin is 30-100 mgKOH/g.
2. The scratch-resistant epoxy modified polyester back paint for the high-coating-rate coiled material as claimed in claim 1, wherein in the esterification reaction in the step (1), the ratio of the mole number of hydroxyl groups contained in the dihydric alcohol to the mole number of carboxyl groups contained in the dibasic acid is 1: 1.1-1.5.
3. The scratch-resistant epoxy modified polyester back paint for the high-coating-rate coil material as claimed in claim 1 or 2, wherein in the ring-opening polymerization reaction in the step (2), the ratio of the number of moles of carboxyl groups contained in the linear carboxyl-terminated polyester resin prepolymer to the number of moles of epoxy groups in the epoxy resin is 1: 0.6-0.9.
4. The scratch-resistant epoxy modified polyester back paint for the high-coating rate coiled material as claimed in claim 1 or 2, wherein the dibasic acid is one or more of phthalic anhydride, isophthalic acid, terephthalic acid, hexahydrophthalic anhydride, adipic acid, 1, 4-cyclohexanedicarboxylic acid and 1, 2-cyclohexanedicarboxylic acid; the dihydric alcohol is one or a mixture of more of neopentyl glycol, methyl propanediol, 1, 4-butanediol, 1, 6-hexanediol, hydroxypivalic acid neopentyl glycol monoester, 3-methyl-1, 5-pentanediol, ethyl butyl propanediol, 1, 4-cyclohexanedimethanol, 1, 2-cyclohexanedimethanol and 2,2, 4-trimethyl-1, 3-pentanediol.
5. The scratch-resistant epoxy modified polyester back paint for the high-coating-rate coiled material as claimed in claim 1, wherein the mass ratio of the branched polyester resin to the base material is 10: 90-20: 80; wherein, the base material comprises epoxy modified polyester resin, branched polyester resin and a curing agent.
6. The scratch-resistant epoxy modified polyester back paint for the high-coating-rate coiled material as claimed in claim 1, wherein the curing agent is amino resin; the amino resin is at least one of methylated urea-formaldehyde resin, butylated urea-formaldehyde resin, fully methylated amino resin, partially methylated amino resin, butylated amino resin and high imino amino resin; the mass ratio of the curing agent to the base material is 15:85-20: 80.
7. The preparation method of the scratch-resistant epoxy modified polyester back paint for the high-coating rate coiled material according to any one of claims 1 to 6, comprising the following steps:
step (1): mixing 30-50% of epoxy modified polyester resin, a dispersant, pigment and filler and wax powder, adding 30-50% of mixed solvent, grinding to obtain slurry, wherein the slurry is sanded to be less than 20 mu m;
step (2): adding the rest of epoxy modified polyester resin, branched polyester resin and the rest of auxiliary agent into the slurry and mixing; and then adding the curing agent and the residual mixed solvent, mixing and filtering to obtain the epoxy modified polyester back paint.
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